The invention relates to a pre-sintered blank for dental purposes based on lithium metasilicate glass ceramic which is suitable in particular for the preparation of dental restorations.
Reports on the use of pre-sintered blanks in dentistry have already been made in the state of the art.
WO 2010/010087 describes porous silicate-ceramic shaped bodies which are processed to form veneers for dentistry. The shaped bodies should have a particular density in order to prevent damage during the machining with milling or grinding systems, e.g. due to the material bursting, and should be suitable for the selected system.
U.S. Pat. No. 5,106,303 describes the preparation of tooth crowns and inlays by copy milling of compacted ceramic bodies which can optionally be pre-sintered. To achieve the desired geometry, the bodies are milled to an enlarged shape in order to take into consideration the shrinkage that occurs during the subsequent sintering to the desired high density. Aluminium oxide, which can optionally include strengthening additives, is used in particular as ceramic material.
U.S. Pat. No. 5,775,912 describes pre-sintered dental porcelain pellets, from which a tooth structure is milled by means of CAD/CAM systems. This tooth structure is embedded in embedding material, sintered and removed from the embedding material in order to produce the desired dental restoration. The dental porcelains used are glass ceramics based on leucite.
U.S. Pat. No. 6,354,836 discloses methods of manufacturing dental restorations using CAD/CAM methods. For this, unsintered or pre-sintered blocks of ceramic material and in particular aluminium oxide and zirconium oxide are used which result in high-strength dental restorations after milling to an enlarged shape followed by dense sintering. However, it is considered to be essential that the temperature differences in the sintering furnace used are smaller than 10° C. in order to ensure that variations in the finally achieved dimensions of the restorations are small.
With the known pre-sintered blanks, the shrinkage occurring during the dense sintering and thus the enlargement factor to be applied depends to a great extent on the pre-sintering temperature applied. Even small variations, such as can occur as a result of an inhomogeneous temperature distribution in the sintering furnace, result in different shrinkages during the dense sintering. However, these shrinkages do not allow the desired small tolerances in the dimensions of the produced dental restoration.